Band-pass signal transmission system



N. KORMAN ETAL 2,510,022

BAND PASS SIGNAL TRANSMISSION" SYSTEM 2 Sheets-Sheet 1 May 30, 1950 g Filed Mazich 15, 1944 N 1 1% a Z 7 Z1 Fig- 1 RF 4 sad/:05 I v LOflD I E I v L Z a N IQQENTORE all/[wad arm wl 6:50

4 TIE/ENE) y 30, 1950 N. 1. KORMAN ET AL 2,510,022

BAND PASS SIGNAL TRANSMISSION SYSTEM Filed March 15 1944 2 Sheets-Sheet 2 INVENTOR5 K WWI/form v zdzr'l 6.50 F 912 w W Q Patented May 30, y 1950 UNITED 1?KTENT .1.QYFFICE \BAND-PASS'SIGNALTRANSMISSION .SYSTZEM. a.

err-Nathaniel IuKQrman, Camdcmand Carl G. Sonhe r r, Hsddonfie N J ass norst charli ..Am ric n .eorroratipnp s ie e- Application March 15, 1944, Seriai' No. 526,846

10. Cl ims. :1

JLhis invention 'relates generally to ,;.signal @transmission. systems and more particularly to improved methods of and-meanszflfor matching a wload: to a a signal transmission vline at: two-different operating :frequencies. eIt -is, W611: known that a fiload connected at the end of a transmission line may Ice-matchedby casvarietyuof matching-means including shunt -reactors,.equarterwavelength impedance transformers, etc. 2 In gen era1,-When a loadvis-matched n 1305a: transmission Kline .by\- any such means, a 'nperfectmatchimayvbe realized at onlyone oper ating Irequency, thedegreeof mismatch increastingrquite rapid1y=as.theoperating frequency deviatesifronr the matchedairequency.

* The ,instant invention contemplates novel matching ;.-,fneqnency, wave reflections -,One such device," providingcequal. and opposite reflections .to those-caused bytheload, comprises asection of transmissionaline,havingnaiength @WhiCh is an .odd ,number: of quarter. wavelengths ;at:the .origin'alcmatched frequency the section-of .v

vline -.is shunted across the main transmission line ,;andv is short-.circuited atsits endaremote irrom :the

main line. It may be shown that-.:the..-ma'gnitude ofa-theawave reflection icoefiicient. from: the; load atany frequency F1. ,which'differs-from theoristhe reflection:coefficientmf the halffWaVesee- $1011 of transmission line. equals the derivative. of

ina1-. line; matching jfr equencyc-Fo. by; an; amount AF ;is

1+4z cot H Nyhere' z is; the ratio; Ofxathe;icharacteristic impedance 21 of the stubgrlineto the-characteristic equal the magnitude, 6f the. reflection from the vload. .ltthggnmaybe. shownthatii the quarter wave. stub line is connected tovthe, main transmission line at. a, distance. equaluto (2) cos P (1R) .1 It amines?voltagem ximums ieem i transmission line in thed ection of the gen erater s eflections hetv veen a line stub enema she rri' b ..sene d an fii r tinsth wi h artene a n st s th exigis snatch r is u as F tith aeeit n watche Ir ,sm nc E Amen i et e 9i. ep li hin hem t .101 alee 1 1a t amme iwi 1s tW Qp 'a i i eq ee w i sthe-t s e. hat s h atch n rbeas qm he c k i w r va i e .e th 'r ee e eee ei 'c he P i inal.isa shine re uee TF e i t l e This ma be a cem ieh sin Pr b Wel 's-1 any s bstantially non-dissipative device h of re ses?- re esfi s tth O in l matc ing frequency F0 as, for example, the shunt; stub m the;m th9 ;fi 9 b e heret r Anethe racti l r aliz tmn o the inve io il l sshan'e s eha cwa el n fi t ri ie l match n f equen F t n. it e mai transmission line to a, d i1ierent characte,ristic Vietnamese-ea f t flb le pur ma transmissio line. This arrangement will-have no efiectrupon -i the- 'ne matching at the Ori inal .,matching frequencygFo. It can be shown that the derivative of the reflection cqelffic ient of this realize .theydesired.1refiection coefficient, it is necessary ton-choose 2102 vso that the derivative of the reflection coefficient of: the load, and to'iocate ;the half wave-length sectionof line sothatrelfiections cancel; at frequencies."ofthemorderaof the second mentioned frequency; F1.

The inventionsthus Igene'raliy.:.1describednmay bereaiizedby means ofany reactive devicef resi onant at the 'lorigina'lflin'e matchingffrequency F0 wherebysthe supplemental resonant-device connected to the line has no effect upon the original match of the frequency F0. It should be understood that the invention may be applied to equal advantage to transmission line systems employing open lines, coaxial transmission lines or waveguides. Structures adapted to the application of the invention for the various types of signal transmission lines will be described in detail hereinafter by reference to the accompanying drawings.

Among the objects of the invention are to provide an improved method of and means for matching a load to a signal transmission line at two adjacent operating frequencies. Another object of the invention is to provide an improved method of and means for matching a load to a signal transmission line simultaneously at two slightly dilferent signal frequencies. A further object of the invention is to provide an improved method of and means for matching a load to a signal transmission line simultaneously at tWo closely related operating frequencies by connectmg a resonant device to said line to provide equal magnitude and oppositely-phased reflections on said line to those reflections provided by the load at one of said operating frequencies.

Other objects of the invention are to include novel methods of and means for matching a load to a signal transmission line at two operating signal frequencies by tuning said load to said transmission line at one of said frequencies, and by connecting to said line at least one reactive device resonant at said one frequency and providing a reflection of equal magnitude but of opposite phase on said line to those provided by said load at the other operating signal frequency. Another object of the invention is to provide an improved method of and means for matching a load to a coaxial transmission line at two operating signal frequencies. An additional object of the invention is to provide an improved method -,of and means for matching a load to a waveguide transmission system at two operating signal frequencies.

The invention will be described further by reference to the accompanying drawings of which Figure 1 is a schematic circuit diagram of one embodiment of the invention; Figure 2 is a schematic circuit diagram of a second embodiment of the invention; Figure 3 is a schematic circuit diagram of a first modification of the first embodiment of the invention illustrated in Figure 1 adapted to use with coaxial transmission lines; Figure 4 is a schematic circuit diagram of a first modification of the second embodiment of the invention adapted to coaxial transmission lines; Figure 5 is a schematic diagram of a second modification of the first embodiment of the invention for waveguide transmission systems; Figure 6 is a schematic diagram of a second modification of the second embodiment of the invention for waveguide transmission systems; Figures 7 and 8, are graphs illustrating the matching characteristics of a load matched to a transmission line at a single operating frequency; Figures 9 and 10 are graphs illustrating the matching of a load to a transmission line at two operating frequencies and Figures 11 and 12 are graphs illustrating the matching of a load to a transmission line of the type illustrated in Figures 2, 4 and 6. Similar reference characters are applied to similar elements throughout the drawings.

Referring to Figure 1, a source of signal energy I is connected to a load 2 by means of a balanced transmission line 3 having a characteristic line impedance .20. The load 2 is matched to the transmission line 3 at a first operating frequency F0 by means of a transmission line stub comprising the conductors 4, 5 each having one end connected to the main transmission line 3 adjacent the load 2. The stub line 4, 5 is tuned by means of a shorting bar 6. The characteristic impedance of the stub line need not be equal to that of the main transmission line characteristic impedance e0.

A second tuning stub comprising the conductors i, 8, short-circuited at their remote ends, and having a length which is any odd multiple of one quarter wavelength at the first operating frequency F0, or in other words has a characteristic impedance zi determined as explained heretofore. The connection of the second quarter-wave tuning stub l, 8 to the main line conductors 3 is made at a point on the main line 3 which is a predetermined distance in the direction or the signal source I from a voltage antinode of the wave reflections from the load 2 at a second adjacent predetermined operating frequency F1.

The point of connection of the second tuning stub, comprising the short-circuited quarterwave conductors 1, 8, is adjusted along the main transmission line 3 until wave reflections are produced which are equal in magnitude and opposite in phase to wave reflections on the line provided by the load 2 at the second operating frequency. Since the second tuning stub i, 8 is quarter-wave resonant at the first operating frequency F0, the connection thereof to the main transmission line 3 does not afiect the match of the load 2 to the main transmission line at the first operating frequency F0.

In Figure 2 the signal generator I is connected to the load 2 through a balanced transmission line 3 having a characteristic impedance 20, and in which is inserted a second section of transmission line [0 having a characteristic impedance 21 and a length corresponding to any integral number of half wavelengths at the first matched frequency F0. As in the circuit of Figure 1, the load 2 connected to one extremity of the main transmission line 3 is matched to the line by means of a tuning stub comprising the conductors 4, 5 and the shorting bar 6. As explained heretofore, the position of the half wave section of transmission line H], having a characteristic impedance 21, with respect to the other seriallyconnected portions of the main transmission line 3, having a characteristic impedance 20, is determined in the manner described heretofore, in order to provide wave reflections of equal magnitude and opposite phase at a second operating frequency F1 to the reflections caused on the main transmission line 3 by the load 2 at said second frequency.

Figure 3 is similar in all respects to the circuit of Figure 1 with the exception that the main transmission line 3 comprises a coaxial transmission line having an inner conductor ll and a coaxially disposed outer conductor l2. Similarly, the tuning stub for matching the load 2 to the coaxial line 3 comprises a coaxial line stub having an inner conductor l4 coaxially disposed within an outer conductor I5 and tuned by an adjustable shorting plug [6.

A second quarter-wave section of coaxial line comprising an inner conductor I! and an outer conductor l 8,.shorted at their remote:.ends,-.:is connected .to' the .m'ain'l. transmission line. 3. JIhe T-loeation of'the second quarter wave. stub 11,48 is'determined as described. heretofore with .re-

spect to apointoi voltage maximum otthe wave frequency for. embodimentsofapplicantsfizinvene reflections onthemaintransmission line 3 provided by the load 2 at asecondoperating-frequency F1. The characteristic:impedance 21 of -thesecond. quarter-waveline l I, 18s with respect td the characteristic impedanceeu of the main. l0.

.hood. of. frequency In.

- transmission line .3 maJSO :is determined: as .-.explained heretofore, to provide wave reflections; of equal magnitudeand oppositephase on: thesmain .line3 tothose provided bytheload 2 atz the second operating frequency-F1.

. Figure dais-similar to..-the:circuit1of EigureiZ but coaxial transmission. lines; are zi -substitut'ed throughout" ion the open balanced: lines. ofiithe circuit of Figure-12in the. sameamanner; as. de-

scribedheretofore in :the circuit of Eignre 3.

Figure 5 issimilar to thecircuits or" Figureszl 1 and B-but waveguides. are'substitutediorthexopen balanced lines of the circuitof. Figure 1:. and for the. coaxial linessof the v'circuitr-oifiE'igure 3. main waveguide? 23, having. ai,;characteristic. impedance 20, connects ithesignal generator 1 l -to the load l'lheia'load .zciszatuned'z to match zthe waveguide .23 at: a...firstf..operatingafrequency F0 by any :one: of the .well known means, such: as a tuning stubz ie having anlongitudinallyeadjustable, plug. '2 85 disposed .therein.

A second quartert wave resonant'waveguidestub 21- having a characteristic impedanceszig provides equal magnitude and tfoppositely phased wave reflectionstinitheimain transmission waverload at said i second. frequency; "said second means :comprisinga second line .1 having; a surge impedanne hearing a predeterminedratio tothe :surge .guide 23 .to'thosezprovidedbnathe load: Z- -in' the main waveguide; 23: at a: secondeoperating-lfrw Lquency F1, as: described .:in-.detai1@heretoiore.

- Figure 6 is l similar. ;to.zthe; circuits. of; -Figures'- 2 and 4 but waveguides. ofdifferent:-character-is- ..tic impedance-2o. and. 21?: are-.lsubstituted for'ithe open balanoed lines of;the.;circuit: oi Figure 2. and for the coaxial lines. of...the: circuit-sci FrEli'guret. 4. Matching oiethe load. 2 to .thezmainawaveguide :23 at the first operatingifre nencycFocis.accomplished by means or. a; conventional-tuningiascrew 2| extendingwithin....the;.mainv waveguide: zeoad'jacent. theload 2.

Itshould be.understood.-that .theload. matching -m'eans at. the first: operatingairequency Fol illustratedin. thedevices of Figures: 5 :.and 6:.may;:;ii desired, beiinterc-hangeds o replaced. byizother .types oicmatching devicesezsincea the; particular .types illustrated and'describedare disclosed here- ;inmerely for the oiir-pose-oi showing the' various types of matching unitsrin commonuse.

. Figure '7 shows .the'magnitude oi the reflection coefiicient as: a function of frequency on artransmission line wherein-the load .-is..m'atched. :to .the

line at onlyone operating; frequency.:...as;is cusmission-line. of the type including: the novel :fea-

.tures of applicants inventionrw-herein the. load: is matched to the transmission line at two closely related predetermined :operating .frequencies: F0, .F1,-thereby providing band-pass goperationionthe .The graphs of Eigureslliandrlzapshow, i-respectively,. the locus of thecomplexv reflection coefficient with. respecato frequency; and the :magnitude .of. the reflection coefficient as: a function-lot vtion wherein one or more derivatives. of the." re- ..fiection. coefficient. vanish atthe first:.:operating frequency F0," thereby providing bandepasssoperationdor a/hand of frequencies .in' thegnei'ghbor- .Thusthe .inventionrdisclosed comprisesxseveral to provide wave. reflections on.the-:main. .trans- .-m-issl0n line-equal 1 in magnitude and. Opposite in yph'ase-to' corresponding wave reflections .from, :the ..load-at the additional-signal frequency toathat lto whichtheload isrinitiallymatched.

We: claim :as our invention: lmlutransmission. line 'f01'; 'il1 erconnectingiia radio frequency.source:.andazloadzincludingiifirst in'eans having; substantially .ithe same: :surgecim- -terinined ufrequency and eecond-meansrhayinge a different surge impedancetham said. lineztnonlltGlJEdiO/Sfiid; iline I at-apredeterminedz distance from voltagev antinode atz a: secondspredetermined frequency thereon to 5 provide wave reflections 011 said line :equal in magnitudes-and opposite in. phasesto wave deflections. from :said

impedance. of said first line such. that at; :least enact. thev derivatives with mespect to frequency of the reflection coeifici'ent: at..-said:first frequency is zero-,-saidfirst-and:saidesecondmeans coroper- .rating-to;;.provide *btlld-Pfl-SSn'illll'iSHllSSiOl'l ever vzsaid line substantially for all freq-uencies; net-ween said first andsaid-secondifreqnencies.

lu l-transmission. line for interconnecting-1a radio frequency-source and azl-oadincluding ifirst .means having substantially the: same: surge .im- :pedance as said .line connected. to; said-rlineazfor .matchingsaiddine to saidwload at-.a firstjpnede- .termined frequency. and second; means having-a different surge impedance :than said i line. serially connected in z saidv -line at 1 ave-predetermined distance irom. a voltage antinode-ata second :predeter-mined. frequency thereon; tog: provide wave reflections on; s'aid..-1ine'; equal in magnituderand opposite in. phaseto wave reflections. lfromz-said load. at said=secondfrequencm said :secondz'means comprising. a; secondiline haying-a" surge'iimpedance' bearing. aapredetermined .ratio-.to:.=the: surge impedance of sa-idafirst. linetisuchiathatat :least one of the derivatives with respect to..=fr.equency of the reflection. coefficient at SaidiflISt frequency ;is zero, saidfirstzand. :second: means co-operating etoeprovide '"bandepassz transmission: over said line substantially for. all drequencies between esaidfirst and saidsecond frequencies.

f 3.:=A transmission ilil'leI for.interconnecting. a radioirequency. .seurce; and. a. loadinelnding; first meanszhaving substantiallykthe samewsurge impedance as said; line" connected :ztov :saiclzclineiafor matching said line atO' z-said-loadt. at .a'. firstmredetermined frequency andssecondmeans' having; a substantially different surge impedance :thansaid ,ifrequency'band extendingerromislightlybelowithe .35 line connected tmsaid line atsaxpredetermined distance from a voltage antinode thereon at a second predetermined frequenc differing slightly from said first frequency to provide Wave reflections on said line equal in magnitude and opposite in phase to wave reflections from said load at said second frequency, said second means comprising a second line having an effective electrical length of an odd number of quarter wavelengths at said first frequency and having a surge impedance substantially different than and bearing a predetermined ratio to the surge impedance of said first line such that at least one of the derivatives with respect to frequency of the reflection coeificient at said first frequency is zero, said first and said second means co-operating to provide band-pass transmission over said line substantially for all frequencies between said first and said second frequencies.

4. A transmission line for interconnecting a radio frequency source and a load including first means having substantially the same surge impedance as said line connected to said line for matching said line to said load at a first predetermined frequency and second means having a different surge impedance than said line serially connected in said line at a predetermined distance from a voltage antinode at a second predetermined frequency thereon to provide wave reflections on said line equal in magnitude and opposite in phase to wave reflections from said load at said second frequency, said second means comprising a second line having an effective electrical length of an integral number of one-half wavelengths at said first frequency and having a surge impedance bearing a predetermined ratio to the surge impedance of said first line such that at least one of the derivatives with respect to frequency of the reflection coeificient at said first frequency is zero, said first and said second means cooperating to provid band-pass transmission over said line substantially for all frequencies between said first and said second frequencies,

5. A transmission line for interconnecting a radio frequency source and a load including first variable reactive means connected to said line i for matching said line to said load at a first predetermined frequency and second means having a different surge impedance than said line connected to said line at a predetermined distance from a voltage antinode at a second predetermined frequency thereon to provide Wave reflections on said line equal in magnitude and opposite in phase to wave reflections from said load at said second frequency, the ratio of the surge impedances of said second means and said line being such that at least one of the derivatives With respect to frequency of the reflection coefficient at said first frequency is zero, said first and said second means cooperating to provide bandpass transmission over said line substantially for all frequencies between said first and said second frequencies.

6. A transmission line for interconnecting a radio frequency sOuICe and a load including first variable reactive means connected to said line for matching said line to said load at a first predetermined frequency and second means having a different surge impedance than said line serially connected to said line at a predetermined distance from a voltage antinode at a second predetermined frequency thereon to provide wave reflections on said line equal in magnitude and opposite in phase to wave reflections from said load at said second frequency, the ratio of the surge impedances of said second means and said line being such that at least one of the derivatives with respect to frequency of the reflection coefiicient at said first frequency is zero, said first and said second means cooperating to provide band-pass transmission over said line substantially for all frequencies between said first and. said second frequencies.

'7. A coaxial transmission line for interconnecting a radio frequency source and a load including first means having substantially the same surge impedance as said line connected to said line for matching said line to said load at a first predetermined frequency and second coaxial means having a different surge impedance than said line connected to said line at a predetermined distance from a voltage antinode at a second predetermined frequency thereon to provide wave reflections on said line equal in magnitude and opposite in phase to wave reflections from said load at said second frequency, said second means comprising a second coaxial line having an effective electrical length of an odd number of quarter wavelengths at said first frequency and having a surge impedance bearing a predetermined ratio to the surge impedance of said first line such that at least one of the derivatives with respect to frequency of the reflection coeflicient at said first frequency is zero, said first and said second means cooperating to provide band-pass transmission over said line substantially for all frequencies between said first and said second frequencies.

8. A wave guide transmission line for interconnecting a radio frequency source and a load including first means having substantially the same surge impedance as said line connected to said line for matching said line to said load at a first predetermined frequency and second waveguide means having a different surge impedance than said line comiected to said line at a predetermined distance from a voltage antinode at a second predetermined frequency thereon to provide wave reflections on said line equal in magnitude and opposite in phase to wave reflections from said load at said second frequency, said second means comprising a second waveguide line having an effective electrical length of an odd number of quarter wavelengths at said first frequency and having a surge impedance bearing a predetermined ratio to the surge impedance of said first line such that at least one of the de-- rivatives with respect to frequency of the re fiection coefficient at said first frequency is zero, said first and said second means cooperating to provide band-pass transmission over said line substantially for all frequencies between said first and said second frequencies.

9. A coaxial transmission line for interconnecting a radio frequency source and a load including first means having substantially the same surge impedance as said line connected to said line for matching said line to said load at a first predetermined frequency and second coaxial means having a different surge impedance than said line serially connected in said line at a predetermined distance from a voltage antinode at a second predetermined frequency thereon to provide Wave reflections on said line equal in magnitude and opposite in phase to wave refiections from said load at said second frequency, said second means comprising a second coaxial line having an effective electrical length of an integral number of one-half wavelengths at said first frequency and having a surge impedance bearing a predetermined ratio to the surge impedance of said first line such that at least one of the derivatives with respect to frequency of the reflection coeflicient at said first frequency is zero, said first and said second means cooperating to provide band-pass transmission over said line substantially for all frequencies between said first and said second frequencies.

10. A waveguide transmission line for interconnecting a radio frequency source and a load including first means having substantially the same surge impedance a said line connected to said line for matching said line to said load at a first predetermined frequency and second waveguide means having a different surge impedance than said line serially connected in said line at a predetermined distance from a voltage antinode at a second predetermined frequency thereto to provide wave reflections on said line equal in magnitude and opposite in phase to wave reflections from said load at said second frequency, said second means comprising a second waveguide line having an effective electrical length of an integral number of one-half wavelengths at said first frequency and having a surge imlpedance bearing a predetermined ratio to the surge impedance of said first line such that at least one of the derivatives with respect to frequency of the reflection coefficient at said first frequency is zero, said first and said second means cooperating to provide band-pass transmission over said line substantially for all frequencies between said first and said second fre- .quencies.

The following references are of record in the file of this patent:

" UNITED STATES PATENTS Number Name Date 2,238,438 Alford Apr. 15, 1941 FOREIGN PATENTS Number Country Date 478,211 Great Britain Jan. 13, 1938 

